Synergistic antimicrobial composition of N-decyl-N-isononyl-N,N-dimethyl ammonium chloride and 2-(decylthio) ethanamine

ABSTRACT

Synergistic antimicrobial combinations comprising N-decyl-N-isononyl-N,N-dimethyl ammonium chloride and 2-(decylthio)ethanamine, or an acid salt therof, are disclosed. Methods for inhibiting microbial growth using these synergistic antimicrobial combinations are also disclosed.

BACKGROUND OF THE INVENTION

1. Field Of The Invention

The present invention relates to synergistic antimicrobial compositionswhich are generally useful for inhibiting microbial growth wherever suchmicrobial growth is found, for example in aqueous systems related to awide variety of industrial applications. More particularly, the presentinvention relates to synergistic admixtures ofN-decyl-N-isononyl-N,N-dimethyl ammonium chloride and2-(decylthio)ethanamine, or an acid salt thereof. Methods for using thesame are also disclosed.

2. Description Of The Background Art

Both N-decyl-N-isononyl-N,N-dimethyl ammonium chloride, referred toherein as N-DIDAC, and 2-(decylthio)ethanamine (DTEA) are knownindividually as antimicrobial agents. The unexpected finding of thepresent invention is that they are synergistic when used in combination.As used herein, the terms "synergy" and "synergistic" refer to instanceswhere the effectiveness of a composition comprising two or morebiocides, such as N-DIDAC and DTEA, exceeds the sum of the efficacies ofthe individual components taken alone. Thus, using a synergisticbiocidal combination may allow for use of a lower overall concentrationof biocide or the realization of an enhanced antimicrobial effect at acomparable dosage.

The use of 2-(decylthio)ethanamine and related compounds, both alone andin conjunction with other antimicrobial agents is known in the art. Forexample, the combination and use of DTEA and2-(2-bromo-2-nitroethenyl)furan is disclosed in U.S. Pat. No. 5,278,188;DTEA and glutaraldehyde in U.S. Pat. No. 5,063,248; DTEA andN-tributyltetradecyl phosphorium chloride in U.S. Pat. No. 4,916,123;DTEA and 2,2-dibromo-3-nitrilo propionamide in U.S. Pat. No. 4,916,159;DTEA and 2-bromo-2-nitropropane-1,3-diol in U.S. Pat. No. 4,914,134;DTEA and dodecylguanidine in U.S. Pat. No. 4,914,130; and DTEA andN-alkyl dimethyl benzyl ammonium chloride in U.S. Pat. No. 4,914,132.

Likewise, the use of N-decyl-N-isononyl-N,N-dimethyl ammonium chlorideand related compounds is known. The synergistic combination of N-DIDACand DTEA, however, is not taught or suggested in the art.

As used herein, the phrases "antimicrobial", "biocide", and "inhibitingmicrobial growth" refer to the killing of, the inhibition of, or thecontrol of the growth of bacteria, yeast, mold and/or algae. A number ofimportant industries have experienced serious adverse effects from theactivity of such biological growth on the raw materials which theyemploy, in their process waters, on various components of theirmanufacturing processes, and in the finished products which theyproduce. Such industries include the paint, wood, textile, cosmetic,leather, tobacco, fur, rope, paper, pulp, plastics, fuel, oil, rubber,and machine industries.

It is contemplated that the synergistic admixture of N-DIDAC and DTEA asdisclosed herein, and the methods for using the same, will be useful invirtually any aqueous system or on any article or product of manufacturein which inhibition of microbial growth is desired, absent compatibilityproblems. Suggested applications of the synergistic antimicrobialcombinations of the present invention include, for example: inhibitingthe growth of bacteria and fungi in aqueous paints, adhesives, latexemulsions, inks and joint cements; preserving wood; preserving cuttingoils and metal working fluids; controlling slime-producing bacteria andfungi, including yeast and mold, in pulp and paper mills and coolingtowers; as a spray or dip treatment for textiles and leather to preventmold growth; as a component of anti-fouling paints to prevent adherenceof fouling organisms; protecting paint films, especially exteriorpaints, from attack by fungi which occurs during weathering of the paintfilm; protecting processing equipment from slime deposits duringmanufacture of cane and beet sugar, food, foodstuffs and food additives;preventing microorganism buildup and deposits in air washer or scrubbersystems and in industrial fresh water supply systems; controllingmicroorganism contamination in closed loop and recirculating watercooling systems; controlling microorganism contamination and deposits inoil field drilling fluids and muds, and in secondary petroleum recoveryprocesses; preventing bacterial and fungal growth in paper coatingprocesses which might adversely affect the quality of the paper coating;controlling bacterial and fungal growth and deposits during themanufacture of various specialty boards, e.g., cardboard, particle boardand foodgrade board; preventing sap stain discoloration on freshly cutwood of various kinds; controlling bacterial and fungal growth in clayand pigment slurries of various types which are manufactured for lateruse in paper coating and paint manufacturing and which are susceptibleto degradation by microorganisms during storage and transport; as a hardsurface disinfectant to prevent growth of bacteria and fungi on walls,floors, etc.; in swimming pools to prevent algal growth; and to controlbacterial and fungal growth in various cosmetic products. It is furthercontemplated that the synergistic admixture of the present inventionwill be useful in various types of non-aqueous systems as well.

The synergistic antimicrobial composition disclosed in the presentinvention is particularly applicable to slime control in papermakingprocesses. The control of bacteria and fungi in pulp and paper millwater systems which contain aqueous dispersions of papermaking fibers invarious consistencies is especially important. The uncontrolled buildupof slime produced by the accumulation of bacteria and fungi may causeoff-grade production, decreased production due to down-time and greatercleanup frequency, increased raw material usage, and increasedmaintenance costs. The problem of slime deposits is especially criticalin light of the widespread use of closed white water systems in thepaper industry.

Another important area in which the antimicrobial compositions of thepresent invention are particularly useful is in the control of bacterialand fungal growth in clay and pigment slurries. These slurries comprisevarious clays (e.g., kaolin) and pigments (e.g., calcium carbonate andtitanium dioxide) and usually are manufactured at a location separatefrom the end use application. This means that they are generallytransported and stored for later use at the application site. Because ofhigh quality standards for the paper and paint products in which suchslurries are used, it is essential that these clay or pigment slurrieshave a very low microorganism count.

In addition, the synergistic combination of the present invention andmethods of using the same have been found especially useful incontrolling the harmful effects of microorganisms in water or aqueousmedia. Systems which utilize circulating water or aqueous media becomeinfected with microorganisms and experience substantial impairment oftheir efficiency when deposits of the microorganisms build up in thesystem. The deposits coat the walls of tanks and other vessels and anymachinery or processing equipment which is employed and create blockagesin pipes and valves. The deposits also create discolorations and otherimperfections in the products being produced, forcing costly shutdowns.Control of microorganisms in aqueous media is particularly importantwhere them are dispersed particles or fines in the aqueous media, forexample, dispersed cellulosic fibers and dispersed fillers and pigmentsin papermaking, and dispersed pigments in paint manufacture.

Accordingly, them remains a very real and substantial need forantimicrobial compositions capable of effectively controlling and/orinhibiting microbial growth in industrial aqueous systems and onarticles of manufacture. Because of increasing environmentalregulations, there is still a further need to provide biocidalcompositions having enhanced antimicrobial effect which are effective inlower doses than historically used. Use of lower amounts of biocides hasa favorable impact on the environment, and allows users to realizesignificant cost savings.

SUMMARY OF THE INVENTION

The present invention generally meets the above described needs byproviding synergistic antimicrobial combinations comprisingN-decyl-N-isononyl-N,N-dimethyl ammonium chloride and2-(decylthio)ethanamine (DTEA). The present invention also provides amethod for inhibiting microbial growth in aqueous systems and onarticles of manufacture prone to such growth comprising adding to saidsystems or applying to said articles an effective amount of acomposition comprising: a) N-decyl-N-isononyl-N,N-dimethyl ammoniumchloride; and b) 2-(decylthio)ethanamine

As used herein, the term "effective amount" refers to that amount of acomposition comprising N-DIDAC and DTEA necessary to achieve the desiredlevel of inhibition or control of microbial growth in the aqueous systemor on the article being treated.

DESCRIPTION OF THE INVENTION

The present invention is directed to a synergistic antimicrobialcomposition comprising: a) N-decyl-N-isononyl-N,N-dimethyl ammoniumchloride; and b) 2-(decylthio)ethanamine, or an acid salt thereof,wherein the weight ratio of a) to b), on an active basis, ranges fromabout 1000:1 to 1:1000. The preferred salt of 2-(decylthio)ethanamine is2-(decylthio)ethanamine hydrochloride. The present invention is furtherdirected to a method for inhibiting microbial growth in an aqueoussystem or on an article of manufacture prone to such growth, whichmethod comprises treating said system or said article with an effectiveamount of an antimicrobial composition comprising: a)N-decyl-N-isononyl-N,N-dimethyl ammonium chloride; and b)2-(decylthio)ethanamine, or an acid salt thereof, wherein the weightratio of a) to b), on an active basis, ranges from about 1000:1 to1:1000.

In accordance with the present invention, the weight ratios of the twocomponents of the synergistic combination are dictated by the dosagelevels of each component which demonstrate synergism, based on 100%active ingredient, relative to each end use application. Typically, theweight ratio of component a), N-DIDAC, and component b), DTEA, rangesfrom about 1000:1 to 1:1000 on an active basis, preferably from about50:1 to 1:50, more preferably from about 7:1 to 1:7. As will beunderstood by one skilled in the art, however, the synergistic weightratio of the two components generally varies to some extent depending onthe application and the organism being controlled. For example, a higherratio of N-DIDAC to DTEA might be more effective in one application,while a higher ratio of DTEA to N-DIDAC might be more effective inanother application. The N-DIDAC/DTEA composition has been foundparticularly effective against bacteria when used in a weight ratio ofbetween about 7:1 to 1:7.

An effective amount of a synergistic combination of N-DIDAC and DTEAshould be added to the aqueous system being treated. At least about 0.1parts per million (ppm), based on the weight of water in the systembeing treated, of the synergistic combination described above should beadded. Preferably, between about 5 ppm and about 500 ppm of N-DIDAC andbetween about 10 ppm and 250 ppm of DTEA, based on the weight of waterin the system being treated, are added. More preferably, between about 5ppm and 62 ppm of N-DIDAC and between about 10 ppm and 31 ppm of DTEA,based on the weight of water in the system being treated, are added. Itis well within the ordinary skill of one practicing in the art todetermine the effective amount of biocide for a given system based onvarious system parameters including but not limited to the size of thesystem, pH of the system, the types of organisms present and the amountof control desired.

Likewise, an effective amount of a synergistic combination of N-DIDACand DTEA should be applied to the article of manufacture being treated.Generally, a solution of the synergistic antimicrobial combinationdescribed above having a concentration of at least 0.1 ppm isincorporated into, sprayed or poured onto, used to dip, or otherwiseapplied, for example by dipping or submersing, to the substrate beingtreated in order to prevent growth of bacteria, mold, yeast and algae.Again, it is well within the ordinary skill of one practicing in the artto determine the effective amount of biocide to apply to a given articleof manufacture being treated and to determine suitable modes ofapplication.

The active ingredients of the synergistic antimicrobial compositions ofthe present invention may also be used in diverse formulations: solid,including finely divided powders and granular materials; as well asliquid, such as solutions, emulsions, suspensions, concentrates,emulsifiable concentrates, slurries and the like, depending upon theapplication intended, and the formulation media desired. Further, whenthe synergistic antimicrobial combinations are liquid, they may beemployed neat or may be incorporated into various formulations, bothsolid and liquid, as an adsorbate on suitable inert carriers such astalc, clays, diatomaceous earth and the like, or water and variousorganic liquids such as lower alkanols, kerosene, benzene, toluene, andother petroleum distillate fractions or mixtures thereof. N-DIDAC iscommercially available in liquid form from Lonza Inc, Fair Lawn, N.J. asBardac® 2170, which contains 70% active N-DIDAC. DTEA is commerciallyavailable from Dow Chemical Company, Midland, Mich. in liquid form.

To prepare a synergistic composition under this invention an effectiveamount of each active ingredient should be combined in a suitablecarrier such as water, organic solvents and the like. The preparation ofsuch a composition is within the ordinary skill of one practicing in theart.

It will also be understood by one skilled in the art that thesynergistic antimicrobial combination disclosed herein may be used incombination with other antimicrobial materials. For example, thecombination can be combined with other fungicides and bactericides inappropriate concentrations and in appropriate instances so as to combinethe action of each to obtain particularly useful results. Suchcombinations might find particular application in the preparation ofgermicidal soaps, in the production of cosmetics and aqueous coatingsand in combating paper mill microbial slime accumulations. It is clearalso that the synergistic antimicrobial combination of the presentinvention can be combined with other algicidal agents as well.

In accordance with the present invention there is still further provideda method of inhibiting the growth of at least one of: bacteria, yeast,mold and algae. According to the methods of the present invention, thisgrowth is inhibited in aqueous systems or on articles or products ofmanufacture prone to such growth. These methods comprise adding to theaqueous system or treating the article or product containing saidbacteria, yeast, mold and/or algae with an effective amount of asynergistic combination of N-DIDAC and DTEA. This addition can beaccomplished either by simple addition of N-DIDAC and DTEA together as asingle admixture, or by addition of the two components separately. Suchseparate administration can either be at the same time or at differenttimes. The net effect will be the same--the system, article or productbeing treated will ultimately have incorporated therein or have appliedthereto the desired dosage concentration of each component.

Further, the compositions of the present invention are believed to beeffective irrespective of the method of application. For example, theantimicrobial compositions described herein can be added to a systembeing treated via a low level, continuous feed practice, asemi-continuous feed practice or through slug feeding. All of thesefeeding practices will be familiar to one having ordinary skill in theart. Slug feeding is particularly effective and therefore is a preferredmanner of employing the methods of the present invention. This type offeed allows the user to monitor the microorganism concentration in thesystem and feed product only when microorganism concentrations increase.The user realizes a cost savings by feeding an effective amount ofN-DIDAC and DTEA only when needed.

As noted above, the present invention is based upon the discovery thatuse of N-DIDAC in conjunction with DTEA produces synergistic results andis effective in controlling the growth of bacteria, yeast, mold andalgae in a variety of industrial and other applications. The utility ofthe synergistic antimicrobial combination disclosed herein derives fromits versatility both in the numerous industries in which it can beapplied, as well as the numerous microorganisms against which it iseffective. In particular, the large economic losses in papermakingoperations caused by the accumulation of bacterial and fungal slimes invarious parts of the system can be eliminated to a significant extent byuse of the synergistic combination described herein.

The superior antimicrobial activity of the synergistic antimicrobialcombination of N-DIDAC and DTEA has been confirmed using standardlaboratory techniques. The antimicrobial combination has been foundeffective, for example, in inhibiting bacterial growth including but notlimited to Klebsiella pneumoniae and Escherichia coli and has been foundto be particularly effective against Pseudomonas aeruginosa. Thecombination is also believed to be effective against other aerobicbacteria, such as Bacillus sp., Staphylococcus sp., Flavobacterium sp.,Enterobacter sp., and Xanthomonas sp., anaerobic bacteria, other freshwater organisms such as filamentous bacteria, fungi including but notlimited to various species of Candida and Saccharomyces and white andpink yeasts, and various species of algae.

EXAMPLES

The following examples are set forth to illustrate the present inventionand should not be construed as limiting the invention in any way.

Example I

The biocidal efficacy in microtiter tests of the antimicrobialcomposition of the present invention is demonstrated below. Threedifferent bacterial strains, Klebsiella pneumoniae, Escherichia coli,Pseudomonas aeruginosa, as well as a mixture of all three of thestrains, were used.

Each of the three bacteria were separately grown on Standard MethodsAgar (STM) plates and incubated at 37° C. for a period of between about24-48 hours. The bacteria were then swabbed from their respective STMplates and suspended in 50 ml of double strength trypticase soy broth(2×TSB) and incubated again at 37° C. for 24 hours; each organism wasincubated in a separate tissue culture flask. The 2×TSB was prepared bymixing about 30 grams of trypticase soy broth powder in about 1000 ml ofdeionized water which had been autoclave sterilized. Following the 24hour incubation of each of the organism suspensions, the suspensionswere diluted in a ratio of 1:10 with additional 2×TSB. Samples from eachof these diluted cultures were then used in the microtiter test. Toprepare the mix of all three of the organisms, an equal amount,approximately 10 ml, of each of the diluted cultures was mixed togetherin a separate tissue culture flask. Samples from this mixture were thenused in the microtiter test.

An 8× stock solution of DTEA to use in combination with N-DIDAC wasprepared by dissolving about 5.3 grams (g) of 15% active DTEA in about100 ml of deionized water. A 4× stock solution of DTEA to use incombination with N-DIDAC was prepared in the same manner only using0.0267 g of DTEA. A 4× stock solution of DTEA to use alone was preparedin the same manner only using 2.67 g of DTEA. The DTEA used in theexamples was obtained from Dow Chemical, Midland, Mich. as AntimicrobialDTEA 15%. An N-DIDAC 8× stock solution to use in combination with DTEAwas prepared by dissolving about 1.0 g of about 80% active Bardac 2180in about 100 ml with deionized water. A 4× stock solution of N-DIDAC touse in combination with DTEA was prepared in the same manner only using0.005 g Bardac 2180. The 4× stock solution of N-DIDAC to use alone wasprepared in the same manner only using 0.5 g of Bardac 2180. The Bardac2180 was obtained from Lonza, Inc., Fair Lawn, N.J.

Eight microtiter plates were used in the example, each microtiter platehaving 8 rows, A-H, and 12 columns, 1-12. The amount of each biocide ineach well of the eight plates is depicted below.

                                      TABLE 1                                     __________________________________________________________________________    AMOUNT OF EACH BIOCIDE IN WELLS OF MICROTITER PLATES 1-8                                  COLUMN CONCENTRATIONS (ppm Active)                                PLATE #                                                                            BIOCIDE                                                                              1  2  3  4  5 6 7 8 9 10                                                                              11                                                                              12                                      __________________________________________________________________________    1,5  N-DIDAC (4X)                                                                         1000                                                                             500                                                                              250                                                                              125                                                                              62                                                                              31                                                                              16                                                                              8 4 2 - +                                            DTEA (8X)                                                                            10 10 10 10 10                                                                              10                                                                              10                                                                              10                                                                              10                                                                              10                                                                              - +                                       2,6  N-DIDAC (8X)                                                                         10 10 10 10 10                                                                              10                                                                              10                                                                              10                                                                              10                                                                              10                                                                              - +                                            DTEA (4X)                                                                            1000                                                                             500                                                                              250                                                                              125                                                                              62                                                                              31                                                                              16                                                                              8 4 2 - +                                       3,7  N-DIDAC (8X)                                                                         0  0  0  0  0 0 0 0 0 0 - +                                            DTEA (8X)                                                                            1000                                                                             500                                                                              250                                                                              125                                                                              62                                                                              31                                                                              16                                                                              8 4 2 - +                                       4,8  N-DIDAC (4X)                                                                         1000                                                                             500                                                                              250                                                                              125                                                                              62                                                                              31                                                                              16                                                                              8 4 2 - +                                            DTEA (4X)                                                                            0  0  0  0  0 0 0 0 0 0 - +                                       __________________________________________________________________________

As is illustrated in the table above, the amount of DTEA in the wells ofplates 1 and 5 and the amount of N-DIDAC in the wells of plates 2 and 6were varied in a serial dilution series ranging from 1000 ppm active to2 ppm active while the other component's concentration was kept at 10ppm active; plates 3 and 7 represented use of DTEA alone, while plates 4and 8 represented the use of N-DIDAC alone. Plates 3 and 4, and 7 and 8were used to determine the minimum amount of each biocide which, whenused alone, would inhibit microbial growth. No biocide was added to thewells of column 12 in any of the plates, which represented an organismcontrol, or positive control. This positive control was run to ensurethat the organisms were capable of growing in the environment provided.No bacteria were added to the wells of column 11 in any of the plates,which represented a broth control, or a negative control. This was doneto ensure that there was no contamination of the plates. In each of the8 microtiter plates Pseudomonas aeruginosa was added to rows A and B,Klebsiella pneumoniae to rows C and D, Escherichia coli to rows E and F,and the mix of all three bacteria to rows G and H.

Plates 1-4 were used to determine the minimum inhibitory concentration(MIC) for each biocide combination against each bacteria strain. The MICis the least amount of biocide needed to prevent growth in the well,with growth being defined as a turbidity in the medium or a "pellet" ofcells which came out of the medium and settled at the bottom of thewell.

Plates 5-8 were then subcultured from plates 1-4, respectively, at 24hours following biocide addition. Subculturing was done to determine theminimum biocidal concentration (MBC). The MBC is the lowestconcentration of biocide that results in no growth after subculturingand subsequent incubation.

All of the microtiter plates including the MIC plates and the MBC plateswere incubated for 24 hours at 37° C. Following the 24 hour incubationperiod, the presence or absence of growth in each well of the plates wasdetermined. Growth in the microtiter plates was determined with aDynatech MR-5000 microplate reader, available from DynatechLaboratories, Chantilly, Va., the use of which will be familiar to onehaving ordinary skill in the art. The presence or absence of growth ineach well, along with the concentration of biocide in each well, wasthen used to determine the synergistic properties of the biocidecombinations. The synergistic properties were evaluated by determiningthe Kull value, or K value; the K value was determined for each of thebacteria tested. The method for calculating K value is well known tothose skilled in the art. In this example, the K value was determined bythe following formula: ##EQU1## where " DTEA! In Combination" means theconcentration of DTEA which, when used in combination with N-DIDAC,resulted in inhibition of microbial growth;

" N-DIDAC! In Combination" means the concentration of N-DIDAC which,when used in combination with DTEA, resulted in inhibition of microbialgrowth;

" DTEA! Alone" means the concentration of DTEA which, when used alone,resulted in inhibition of microbial growth; and

" N-DIDAC! Alone" means the concentration of the N-DIDAC which, whenused alone, resulted in inhibition of microbial growth.

A K value of less than 1 indicates synergy between the two biocides, a Kvalue of greater than 1 indicates antagonism between the two biocides,and a K value equal to 1 indicates an additive effect of the twobiocides.

The K values determined for each of the organisms used in the exampleare recorded in Tables 2 through 5.

                                      TABLE 2                                     __________________________________________________________________________    "K" VALUES OF PLATE 1 (MIC)                                                                           DTEA! In                                                                             N-DIDAC! In                                                DTEA!                                                                               N-DIDAC!                                                                           Combination,                                                                         Combination,                                                                         K  Weight Ratio                          Organism   Alone, ppm                                                                          Alone, ppm                                                                          ppm    ppm    Value                                                                            N-DIDAC:DTEA                          __________________________________________________________________________    Pseudomonas aeruginosa                                                                   100   31     10    16     0.62                                                                             1.6:1                                 Klebsiella pneumoniae                                                                    9.4   12    <10    <2     <1.2                                                                               1:5                                 Escherichia coli                                                                         6.2   12    <10    <2     <1.8                                                                               1:5                                 Mixture of above                                                                         75    31     10    12     0.52                                                                             1.2:1                                 three 31                                                                      __________________________________________________________________________

                                      TABLE 3                                     __________________________________________________________________________    "K" VALUES OF PLATE 2 (MIC)                                                                           DTEA! In                                                                             N-DIDAC! In                                                DTEA!                                                                               N-DIDAC!                                                                           Combination,                                                                         Combination,                                                                         K  Weight Ratio                          Organism   Alone, ppm                                                                          Alone, ppm                                                                          ppm    ppm    Value                                                                            N-DIDAC:DTEA                          __________________________________________________________________________    Pseudomonas aeruginosa                                                                   100   31    20      10    0.52                                                                               1:2                                 Klebsiella pneumoniae                                                                    9.4   12    <2     <10    <1.0                                                                               5:1                                 Escherichia coli                                                                         6.2   12    <2     <10    <1.2                                                                               5:1                                 Mixture of above three                                                                    75   31     8      10    0.43                                                                             1.2:1                                 __________________________________________________________________________

                                      TABLE 4                                     __________________________________________________________________________    "K" VALUES OF PLATE 5 (MBC)                                                                           DTEA! In                                                                             N-DIDAC! In                                                DTEA!                                                                               N-DIDAC!                                                                           Combination,                                                                         Combination,                                                                         K  Weight Ratio                          Organism   Alone, ppm                                                                          Alone, ppm                                                                          ppm    ppm    Value                                                                            N-DIDAC:DTEA                          __________________________________________________________________________    Pseudomonas aeruginosa                                                                   100   47     10    62     1.4                                                                              6.2:1                                 Klebsiella pneumoniae                                                                    12.5  16    <10    <2     <0.92                                                                              1:5                                 Escherichia coli                                                                          6.2  16    <10    <2     1.7                                                                                1:5                                 Mixture of above three                                                                   125   94     10    62     0.74                                                                             6.2:1                                 __________________________________________________________________________

                                      TABLE 5                                     __________________________________________________________________________    "K" VALUES OF PLATE 6 (MBC)                                                                           DTEA! In                                                                             N-DIDAC! In                                                DTEA!                                                                               N-DIDAC!                                                                           Combination,                                                                         Combination,                                                                         K  Weight Ratio                          Organism   Alone, ppm                                                                          Alone, ppm                                                                          ppm    ppm    Value                                                                            N-DIDAC:DTEA                          __________________________________________________________________________    Pseudomonas aeruginosa                                                                   100   47    500     10    5.2                                                                              1:50                                  Klebsiella pneumoniae                                                                    12.5  16    <2     <10    0.78                                                                             5:1                                   Escherichia coli                                                                          6.2  16    <2     <10    0.95                                                                             5:1                                   Mixture of above three                                                                   125   94    250     10    2.1                                                                              1:25                                  __________________________________________________________________________

As can be seen from the results of Table 2-5, synergy was demonstratedagainst all three organisms tested, as well as the mix of these threeorganisms.

Example II

Example I was repeated using different concentrations of N-DIDAC andDTEA. N-DIDAC was tested at concentrations of 500, 250, 125, 62, 31, 16,8, 4, 2 and 1 ppm, while the amount of DTEA was held constant at 5 ppm.DTEA was tested at the same concentrations while the amount of N-DIDACwas held constant at 5 ppm. Use of N-DIDAC alone and DTEA alone was alsotested in a serial dilution ranging from 500 ppm to 1 ppm. Results arepresented in Tables 6-9 below.

                                      TABLE 6                                     __________________________________________________________________________    "K" VALUES OF PLATE 1 (MIC)                                                                           DTEA! In                                                                             N-DIDAC! In                                                DTEA!                                                                               N-DIDAC!                                                                           Combination,                                                                         Combination,                                                                         K  Weight Ratio                          Organism   Alone, ppm                                                                          Alone, ppm                                                                          ppm    ppm    Value                                                                            N-DIDAC:DTEA                          __________________________________________________________________________    Pseudomonas aeruginosa                                                                    62   31     5     31     1.08                                                                             6.2:1                                 Klebsiella pneumoniae                                                                     8     8    <5     <1     <0.75                                                                              1:5                                 Escherichia coli                                                                          6    16    <5     <1     <0.90                                                                              1:5                                 Mixture of above three                                                                   125   31     5     31     1.04                                                                             6.2:1                                 __________________________________________________________________________

                                      TABLE 7                                     __________________________________________________________________________    "K" VALUES OF PLATE 2 (MIC)                                                                           DTEA! In                                                                             N-DIDAC! In                                                DTEA!                                                                               N-DIDAC!                                                                           Combination,                                                                         Combination,                                                                         K  Weight Ratio                          Organism   Alone, ppm                                                                          Alone, ppm                                                                          ppm    ppm    Value                                                                            N-DIDAC:DTEA                          __________________________________________________________________________    Pseudomonas aeruginosa                                                                    62   31    31     5      0.66                                                                             1:6.2                                 Klebsiella pneumoniae                                                                     8     8    3      5      1.0                                                                              1:6.2                                 Escherichia coli                                                                          6    16    1.5    5      0.56                                                                             3.3:1                                 Mixture of above three                                                                   125   31    31     5      0.41                                                                             1:6.2                                 __________________________________________________________________________

                                      TABLE 8                                     __________________________________________________________________________    "K" VALUES OF PLATE 5 (MBC)                                                                           DTEA! In                                                                             N-DIDAC! In                                                DTEA!                                                                               N-DIDAC!                                                                           Combination,                                                                         Combination,                                                                         K  Weight Ratio                          Organism   Alone, ppm                                                                          Alone, ppm                                                                          ppm    ppm    Value                                                                            N-DIDAC:DTEA                          __________________________________________________________________________    Pseudomonas aeruginosa                                                                   281   62    5      62     1.02                                                                             12.4:1                                Klebsiella pneumoniae                                                                    8     12    5       3     0.89                                                                               1:1.7                               Escherichia coli                                                                         16    16    5       8     0.81                                                                              1.6:1                                Mixture of above three                                                                   187.5 62    5      62     1.28                                                                             12.4:1                                __________________________________________________________________________

                                      TABLE 9                                     __________________________________________________________________________    "K" VALUES OF PLATE 6 (MBC)                                                                           DTEA! In                                                                             N-DIDAC! In                                                DTEA!                                                                               N-DIDAC!                                                                           Combination,                                                                         Combination,                                                                         K  Weight Ratio                          Organism   Alone, ppm                                                                          Alone, ppm                                                                          ppm    ppm    Value                                                                            N-DIDAC:DTEA                          __________________________________________________________________________    Pseudomonas aeruginosa                                                                   281   62    250    5      0.97                                                                                1:50                               Klebsiella pneumoniae                                                                    8     12    4      5      0.92                                                                             1.25:1                                Escherichia coli                                                                         16    16    4      5      0.52                                                                             1.25:1                                Mixture of above three                                                                   187.5 62    187.5  5      1.08                                                                                1:37.5                             __________________________________________________________________________

What is claimed is:
 1. A synergistic antimicrobial combinationcomprising:a) N-decyl-N-isononyl-N,N-dimethyl ammonium chloride; and b)2(decylthio)ethanamine, or an acid salt thereof, wherein the weightratio of a) to b), on an active basis, ranges between about 7:1 and 1:7.2. A method for inhibiting microbial growth in an aqueous system whichcomprises adding to said system an effective amount of a synergisticantimicrobial combination comprising:a) N-decyl-N-isononyl-N,N-dimethylammonium chloride; and b) 2(decylthio)ethanamine, or an acid saltthereof, wherein the weight ratio of a) to b), on an active basis,ranges between about 7:1 and 1:7.
 3. The method of claim 2, wherein theN-decyl-N-isononyl-N,N-dimethyl ammonium chloride and2-(decylthio)ethanamine are added together as a single composition tothe system being treated.
 4. The method of claim 2, wherein theN-decyl-N-isononyl-N,N-dimethyl ammonium chloride and2-(decylthio)ethanamine are added separately to the system beingtreated.
 5. The method of claim 2, wherein at least 0.1 ppm of thesynergistic antimicrobial composition is added to the system beingtreated.
 6. The method of claim 2, wherein between about 62 ppm and 5ppm N-decyl-N-isononyl-N,N-dimethyl ammonium chloride and between about10 ppm and 31 ppm 2-(decylthio)ethanamine are added to the system beingtreated.
 7. A method of inhibiting microbial growth on an article ofmanufacture which comprises applying to said article an effective amountof a synergistic antimicrobial combination comprising:a)N-decyl-N-isononyl-N,N-dimethyl ammonium chloride; and b)2(decylthio)ethanamine, or an acid salt thereof; wherein the weightratio of a) to b), on an active basis, ranges between about 7:1 and 1:7.8. The method of claim 7, wherein the N-decyl-N-isononyl-N,N-dimethylammonium-chloride and 2-(decylthio)ethanamine are applied together as asingle composition to the article being treated.
 9. The method of claim7, wherein the N-decyl-N-isononyl-N,N-dimethyl ammonium chloride and2-(decylthio)ethanamine are applied separately to the article beingtreated.
 10. The method of claim 7, wherein said synergisticantimicrobial composition has a concentration of at least 0.1 ppm.